JP2011528842A - Separator provided with porous coating layer, method for producing the same and electrochemical device provided with the same - Google Patents

Abstract

  The separator of the present invention comprises a planar nonwoven fabric substrate having a large number of pores; and a porous coating layer formed on a mixture of a large number of inorganic particles and a binder polymer provided on at least one surface of the nonwoven fabric substrate. The nonwoven fabric base material includes pores having an average thickness of 0.5 to 10 μm and a pore length of 0.1 to 70 μm based on the total number of pores. Contains 50% or more. A separator having a porous coating layer according to the present invention uses a non-woven substrate whose pore size is controlled by using an ultrafine thread of a predetermined thickness, and does not increase the loading amount of the porous coating layer. Generation of current can be prevented.

Description

  The present invention relates to a separator for an electrochemical element such as a lithium secondary battery, a method for producing the same, and an electrochemical element having the separator, and more specifically, a mixture of inorganic particles and a binder polymer. The present invention relates to a separator in which a porous coating layer is formed on at least one surface of a nonwoven fabric substrate, a method for producing the separator, and an electrochemical device including the separator.

  Recently, interest in energy storage technology is increasing. As the field of application expands to the energy of mobile phones, camcorders and notebook PCs, and eventually electric vehicles, efforts to research and develop electrochemical devices are becoming more and more concrete. Electrochemical devices are the field that has received the most attention in this respect, and the development of rechargeable batteries that can be charged and discharged has become the focus of interest. Research and development on new electrode and battery designs is underway to improve capacity density and specific energy.

  Among secondary batteries currently in use, lithium secondary batteries developed at the beginning of the 1990s are compared to conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use aqueous electrolyte. It is in the limelight due to its high operating voltage and much higher energy density. However, such a lithium ion battery has safety problems such as ignition and explosion caused by using an organic electrolyte, and has a disadvantage that it is difficult to manufacture. Recent lithium ion polymer batteries have been listed as one of the next generation batteries by improving the shortcomings of such lithium ion batteries, but the battery capacity is still relatively low compared to lithium ion batteries, In particular, the discharge capacity at low temperatures is insufficient, and an improvement to this is urgently required.

  Although the electrochemical devices as described above are produced by many manufacturers, their safety characteristics are different from each other. It is very important to evaluate the safety and ensure the safety of such electrochemical devices. The most important consideration is that the user should not be injured when the electrochemical device malfunctions. For this purpose, the safety standard strictly controls the ignition and smoke of the electrochemical device. ing. In the safety characteristics of an electrochemical element, if the electrochemical element is overheated and thermal runaway occurs or the separation membrane is penetrated, there is a high risk of explosion. In particular, a polyolefin-based porous substrate usually used as a separation membrane for an electrochemical element exhibits a severe heat shrinkage behavior at a temperature of 100 ° C. or more due to material characteristics and manufacturing process characteristics including stretching. There is a problem of causing a short circuit between the anodes.

  In order to solve the safety problem of such an electrochemical device, a porous coating layer is formed by coating a mixture of inorganic particles and a binder polymer on at least one surface of a porous substrate having a large number of pores. A separator was proposed. For example, Patent Document 1, Patent Document 2 and Patent Document 3 disclose a technique related to a separator provided with a porous coating layer formed of a mixture of inorganic particles and a binder polymer on a porous substrate. .

  In a separator having such a porous coating layer, when a non-woven fabric is used as the porous base material, there is a possibility that a leakage current is generated and the insulation of the separator is lowered. When increasing the loading amount of the porous coating layer in order to prevent the occurrence of leakage current, the thickness of the separator increases, which is not suitable for realizing a high capacity battery.

  Accordingly, there is a need for a technique for optimally designing a nonwoven fabric substrate on which a porous coating layer is provided and preventing the occurrence of leakage current while not increasing the loading amount of the porous coating layer.

Korean Patent Publication No. 2007-0019958 Japanese Patent Publication No. 2005-536857 Japanese Patent Publication No. 1999-080395

  Therefore, the problem to be solved by the present invention is to optimize the nonwoven fabric substrate on which the porous coating layer is provided, and to prevent the occurrence of leakage current while not increasing the loading amount of the porous coating layer, and It is in providing the manufacturing method.

  Another problem to be solved by the present invention is to provide a high-capacity electrochemical device including the above-described separator.

  In order to achieve the above object, the separator of the present invention is a planar nonwoven fabric substrate having a large number of pores; and a mixture of a large number of inorganic particles and a binder polymer provided on at least one surface of the nonwoven fabric substrate. A separator including a formed porous coating layer, wherein the nonwoven fabric substrate is formed of ultrafine yarn having an average thickness of 0.5 to 10 μm, and a major diameter of pores is 0.1 to 70 μm (micrometer). Are contained in an amount of 50% or more based on the total number of pores.

In the separator of the present invention, the thickness of the nonwoven fabric substrate is preferably 9 to 30 μm. The loading amount of the porous coating layer on the nonwoven fabric substrate is preferably 5 to 20 g / m ² .

  The above-mentioned separator is a flat nonwoven fabric formed of ultrafine yarn having an average thickness of 0.5 to 10 μm and containing 50% or more of pores having a major axis of pores of 0.1 to 70 μm based on the total number of pores. Preparing a base material; and coating a binder polymer solution in which inorganic particles are dispersed on at least one surface of the non-woven fabric base material, followed by drying.

  Such a separator of the present invention can be used for an electrochemical device such as a lithium secondary electron or a supercapacitor device through a cathode and an anode.

  The separator of this invention can suppress the short circuit between a cathode and an anode with the inorganic particle which exists in a porous coating layer, even when an electrochemical element is overheated by a porous coating layer. In addition, by using a nonwoven fabric base whose pore size is controlled using ultrafine yarn of a predetermined thickness, it is possible to prevent the occurrence of leakage current while not increasing the loading amount of the porous coating layer.

  Therefore, the electrochemical device provided with such a separator not only has excellent thermal safety but also can realize a high capacity.

It is a SEM photograph of the nonwoven fabric base material used for Example 1 of this invention. It is a graph which shows distribution of the pore size formed in the nonwoven fabric base material of FIG. It is the SEM photograph which image | photographed the surface of the separator formed according to Example 1 of this invention. 2 is a SEM photograph of a nonwoven fabric substrate used in Comparative Example 1. It is a graph which shows distribution of the pore size formed in the nonwoven fabric base material of FIG. 4 is a SEM photograph of a nonwoven fabric substrate used in Comparative Example 2. It is a graph which shows distribution of the pore size formed in the nonwoven fabric base material of FIG. Loading weight of the porous coating layer according to Comparative Example 2 is charged and discharged failure profile of the battery is 0 g / m ^2. 6 is a leakage current profile of a battery in which the loading amount of the porous coating layer exceeded 20 g / m ^{2 according} to Comparative Example 1. The charge / discharge path profile of the battery in which the loading amount of the porous coating layer exceeded 5-20 g / m ² and 20 g / m ² according to Example 1, and the loading amount of the porous coating layer according to Comparative Example 2 was 20 g / m ^2. It is the charging / discharging path profile of the battery exceeding this.

  Hereinafter, the present invention will be described in detail. Prior to this, the terms and words used in the specification and claims should not be construed in a normal or lexicographic sense, and the inventor will explain his invention in the best possible way. Therefore, in accordance with the principle that the concept of a term can be appropriately defined, it should be interpreted as a meaning and a concept consistent with the technical idea of the present invention. Therefore, the embodiment described in the present specification and the configuration shown in the drawings are only the most preferred embodiment of the present invention and do not represent all the technical ideas of the present invention. It should be understood that there are various equivalents and variations that can be substituted for these.

  The separator of the present invention comprises a planar nonwoven fabric substrate having a large number of pores, and the nonwoven fabric substrate is formed from ultrafine yarn having an average thickness of 0.5 to 10 μm, preferably 1 to 7 μm. Not only is it difficult to produce a nonwoven fabric formed from ultrafine yarn having an average thickness of less than 0.5 μm, but the mechanical properties of the nonwoven fabric are reduced. In addition, when the average thickness of the ultrafine yarn exceeds 10 μm, it is difficult to control the pore size of the nonwoven fabric, so that it is difficult to form pores having the size and distribution described later.

  Further, the nonwoven fabric substrate contains 50% or more of pores having a pore major diameter (longest pore diameter) of 0.1 to 70 μm based on the total number of pores. Not only is it difficult to produce a nonwoven fabric having a large number of pores having a major axis of less than 0.1 μm, but this may reduce the porosity of the nonwoven fabric and partially hinder the smooth movement of lithium ions. If the long diameter of the pores exceeds 70 μm, the problem of insulation deterioration due to leakage current tends to occur. When increasing the loading amount of the porous coating layer in order to prevent the occurrence of leakage current, the separator becomes thicker, so that it is difficult to implement a high capacity battery.

  By including 50% or more of the pores of the above-mentioned size on the basis of the total number of pores existing in the nonwoven fabric, the object of the present invention can be achieved by optimally designing the configuration and pore size of the nonwoven fabric.

  The ultra-fine yarns forming the nonwoven fabric substrate are polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as aramid, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, and polyphenylene oxide. , Polyphenylene sulfide, polyethylene naphthalene, etc., but is not limited thereto. In particular, in order to improve the thermal safety of the nonwoven fabric substrate, the melting temperature of the ultrafine yarn is desirably 200 ° C. or higher. The thickness of the nonwoven fabric substrate is desirably 9 to 30 μm.

In the separator of the present invention, a porous coating layer is provided on at least one surface of the above-described nonwoven fabric substrate. The porous coating layer is formed of a mixture of a large number of inorganic particles and a binder polymer. Many inorganic particles are connected to each other by a binder polymer, and voids are formed between the inorganic particles. The loading amount of the porous coating layer with respect to the nonwoven fabric substrate is desirably 5 to 20 g / m ² , and if the loading amount is less than 5 g / m ² , a leakage current may be generated. If it exceeds 20 g / m ² , the thickness of the separator increases, and the compatibility with a high-capacity battery may be reduced.

In the separator of the present invention, the inorganic particles used for forming the porous coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles used in the present invention are not particularly limited as long as oxidation and / or reduction reactions do not occur in the operating voltage range of the applied electrochemical device (for example, ⁰ to 5 V on the basis of Li / Li ⁺ ). Not limited. In particular, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolytic solution can be improved by contributing to an increase in the dissociation degree of an electrolyte salt in the liquid electrolyte, for example, a lithium salt.

For the reasons described above, the inorganic particles preferably include high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT). _{), Pb (Mg 3 Nb 2/3} ) O 3 -PbTiO 3 (PMN-PT), hafnia (HfO 2), SrTiO 3, SnO 2, CeO 2, MgO, NiO, CaO, ZnO, ZrO 2, Y 2 There are O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, or a mixture thereof.

Further, as the inorganic particles, inorganic particles having lithium ion transmission ability, that is, inorganic particles containing lithium element but having a function of moving lithium ions without storing lithium can be used. Non-limiting examples of inorganic particles having lithium ion transfer capability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <. y <3), lithium aluminum titanium phosphate _{(Li x Al y Ti z (} PO 4) 3, 0 <x <2,0 <y <1,0 <z <3), 14Li 2 O-9Al 2 O 3 -38TiO ₂ -39P ₂ O _5, such as _(LiAlTiP) x _{O y} series glass (0 <x <4,0 <y <13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2 , 0 <y <3), lithium germanium thiophosphates such as Li _3.25 Ge _0.25 P _0.75 S ₄ (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), i ₃ lithium nitride such as _{N (Li x N y, 0} <x <4,0 <y <2), SiS 2 series glasses, such as _{Li 3 PO 4 -Li 2 S-} SiS 2 (Li _{x Si y S z, 0 <} x <3,0 <y <2,0 <z <4), P 2 S 5 series glass such as _{LiI-Li 2 S-P 2} S 5 (Li x P y S _z , 0 <x <3, 0 <y <3, 0 <z <7) or a mixture thereof.

  In the separator of the present invention, the size of the inorganic particles in the porous coating layer is not limited, but it should be in the range of 0.001 to 10 μm as much as possible in order to form a coating layer with a uniform thickness and appropriate porosity. Is desirable. If it is less than 0.001 μm, the dispersibility may decrease, and if it exceeds 10 μm, the thickness of the porous coating layer may increase, and the probability that an internal short circuit will occur during charging / discharging of the battery due to the too large pore size Becomes higher.

  Moreover, as a binder polymer contained in the porous coating layer, a polymer usually used in the industry for forming a porous coating layer on a nonwoven fabric substrate can be used. In particular, it is desirable to use a polymer having a glass transition temperature (Tg) of −200 to 200 ° C., which is a mechanical property such as flexibility and elasticity of the finally formed porous coating layer. This is because the physical properties can be improved. Such a binder polymer serves as a binder for connecting and stably fixing the inorganic particles or between the inorganic particles and the nonwoven fabric substrate.

  In addition, the binder polymer does not necessarily have ion conduction ability, but when a polymer having ion conduction ability is used, the performance of the electrochemical element can be further improved. Therefore, it is desirable that the binder polymer has a dielectric constant as high as possible. Actually, the degree of salt dissociation in the electrolyte solution depends on the dielectric constant of the electrolyte solvent, and the higher the dielectric constant of the binder polymer, the higher the degree of salt dissociation in the electrolyte. The dielectric constant of such a binder polymer can be in the range of 1.0 to 100 (measurement frequency = 1 kHz), and is preferably 10 or more.

In addition to the functions described above, the binder polymer may have a characteristic of exhibiting a high degree of electrolyte impregnation by being gelled when impregnated with the liquid electrolyte. Accordingly, it is desirable to use a polymer having a solubility index of 15 to 45 MPa ^1/2 , and more desirable solubility indexes are in the ranges of 15 to 25 MPa ^1/2 and 30 to 45 MPa ^1/2 . Therefore, it is desirable to use a hydrophilic polymer having a large number of polar groups rather than a hydrophobic polymer such as polyolefins. If solubility index exceeds ^{15 MPa 1/2} and less than ^{45 MPa 1/2,} which not easily impregnated by conventional battery liquid electrolyte.

  Non-limiting examples of such polymers include polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-trichloroethylene (polyvinylidene fluoride-co-trichloroethylene methacrylate, polymethylmethacrylate, polyacrylonitrile, poly (vinylpyrrolidone), poly (vinyl acetate), poly (ethylene-co-vinyl) copolymer. tate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpolybutyl alcohol , Cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose (carbox) lmethyl cellulose) and the like.

  The composition ratio of the inorganic particles and the binder polymer in the porous coating layer coated on the nonwoven fabric substrate according to the present invention is preferably in the range of 50:50 to 99: 1, and more preferably 70:30 to 95: 5. It is. When the content ratio of the inorganic particles to the binder polymer is less than 50:50, the polymer content is too high, and the pore size and porosity of the porous coating layer may be reduced. When the content of the inorganic particles exceeds 99 parts by weight, the peel resistance of the porous coating layer can be weakened because the content of the binder polymer is too small. The pore size and porosity of the porous coating layer are not particularly limited, but the pore size is preferably in the range of 0.001 to 10 μm, and the porosity is preferably in the range of 10 to 90%. The pore size and porosity mainly depend on the size of the inorganic particles. For example, when inorganic particles having a particle size of 1 μm or less are used, the formed pores also show about 1 μm or less. Such a pore structure will be filled with an electrolyte to be injected later, and the electrolyte thus filled will play a role of ion transfer. When the pore size and porosity are less than 0.001 μm and less than 10%, respectively, it can act as a resistance layer, and when the pore size and porosity exceed 10 μm and 90%, respectively, mechanical properties can be lowered.

  The separator of the present invention may further contain other additives in addition to the aforementioned inorganic particles and polymer as components of the porous coating layer.

  Although the desirable manufacturing method of the separator by this invention is illustrated below, it is not limited to this.

  First, a planar nonwoven fabric base material comprising 50% or more of pores having an average thickness of 0.5 to 10 μm and pores having a major diameter of 0.1 to 70 μm based on the total number of pores Prepare. Nonwoven fabrics having such a configuration can be manufactured by adjusting the diameter and spinning density of nozzles for spinning ultrafine yarns.

  Next, a separator is manufactured by coating and drying a binder polymer solution in which inorganic particles are dispersed on at least one surface of the nonwoven fabric substrate.

  The binder polymer solution in which the inorganic particles are dispersed can be produced by dissolving the binder polymer in a solvent to produce a binder polymer solution, and then adding and dispersing the inorganic particles. A solvent having a solubility index similar to that of the binder polymer to be used and a low boiling point is desirable. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N -Methyl-2-pyrrolidone (NMP), cyclohexane, water or mixtures thereof. It is desirable to crush the inorganic particles after adding the inorganic particles to the binder polymer solution. At this time, the crushing time is appropriately 1 to 20 hours, and the particle size of the crushed inorganic particles is preferably 0.001 to 10 μm as described above. A normal method can be used as the crushing method, and the ball mill method is particularly desirable.

  For example, when a non-woven substrate is coated with a solution of a binder polymer in which inorganic particles are dispersed and dried under a humidity condition of 10 to 80%, a normal coating method known in the art can be used. For example, various methods such as a dip coating, a die coating, a roll coating, a comma coating, or a mixture thereof may be used. Further, the porous coating layer can be selectively formed only on both sides or one side of the nonwoven fabric substrate. The porous coating layer formed in accordance with such a coating method is partially present not only on the surface of the nonwoven fabric substrate but also on the inside thereof due to the properties of the nonwoven fabric substrate.

  Such a separator of the present invention is manufactured as an electrochemical element through a cathode and an anode. At this time, when a polymer that can be gelled at the time of impregnation with the liquid electrolyte is used as a binder polymer component, the electrolyte and polymer injected after the battery is assembled using the separator react to gel. Can be done.

  The electrochemical element of the present invention includes all elements that undergo an electrochemical reaction. For example, all types of capacitors such as primary, secondary batteries, fuel cells, solar cells, or supercapacitor elements (Capacitor). In particular, among the secondary batteries, lithium secondary batteries including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries are preferable.

  The electrode used together with the separator of the present invention is not particularly limited, and can be produced in a form in which an electrode active material is bound to an electrode current collector according to a usual method known in the art. Among the electrode active materials, as a non-limiting example of the cathode active material, a conventional cathode active material conventionally used as a cathode of an electrochemical device can be used, particularly lithium manganese oxide, lithium cobalt oxide, It is desirable to use lithium nickel oxide, lithium iron oxide, or a lithium composite oxide combining these. As a non-limiting example of the anode active material, a conventional anode active material conventionally used as an anode of an electrochemical element can be used, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activation Lithium adsorbents such as activated carbon, graphite or other carbons are desirable. Non-limiting examples of cathode current collectors include foils made from aluminum, nickel or combinations thereof, and non-limiting examples of anode current collectors include copper, gold, nickel or There are foils manufactured from copper alloys or combinations thereof.

The electrolyte that can be used in the present invention is a salt having a structure such as A ⁺ B ⁻ , and A ⁺ is an ion composed of an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ , or a combination thereof. B ⁻ is PF ₆ ⁻ , BF ₄ ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , CH ₃ CO ₂ ⁻ , CF ₃ SO ₃ ⁻ , N (CF ₃ SO ₂ ) _{2 ^{-, C (CF 2 sO 2}} ) 3 - anions or salt, propylene carbonates containing ions a combination thereof, such as (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate ( DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydro Examples include, but are not limited to, those dissolved or dissociated in organic solvents consisting of orchid, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or mixtures thereof. It is not done.

  The electrolyte can be injected at an appropriate stage in the battery manufacturing process according to the manufacturing process and required physical properties of the final product. That is, the present invention can be applied before battery assembly or at the final stage of battery assembly.

  As a process of applying the separator of the present invention to a battery, in addition to a general process of winding, there can be a lamination and stacking process of a separator and an electrode and a folding process.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified in many forms, and the scope of the present invention should not be construed to be limited to the embodiments described later. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

Example 1
Manufacture of separator PVdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene copolymer) and cyanoethyl pullulan were added to acetone at a weight ratio of 10: 2, respectively, and dissolved at 50 ° C. for about 12 hours or more to obtain a polymer solution. Manufactured. BaTiO ₃ powder is added to the produced binder polymer solution so that the binder polymer / BaTiO ₃ = 10/90 weight ratio, and the slurry is obtained by crushing and dispersing the BaTiO ₃ powder using the ball mill method for 12 hours or more. Manufactured. The BaTiO ₃ particle size of the slurry thus produced can be controlled by the size (particle size) of the beads used in the ball mill and the ball mill time. In Example 1, the slurry was pulverized to about 400 nm. The slurry thus produced was coated on a 12 μm thick polyethylene terephthalate nonwoven fabric by dip coating while changing the loading amount. The non-woven fabric used was made of ultrafine yarn having an average thickness of about 3 μm (see FIG. 1), and as shown in FIG. 2, a material having a major axis of less than 70 μm and 100% pores was used. In the present invention, the average thickness of the ultrafine yarn constituting the nonwoven fabric substrate was measured using an SEM photograph, and the pore size due to the pore size and pore distribution was measured according to ASTM F316.

  FIG. 3 is a photograph of the surface of the manufactured separator.

Production of Anode Carbon powder as anode active material, polyvinylidene fluoride (PVdF) as binder, carbon black as conductive material to 96 wt%, 3 wt% and 1 wt%, respectively, as solvent N An anode active material slurry was prepared by adding to -methyl-2-pyrrolidone (NMP). The anode active material slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 μm and dried to produce an anode, followed by roll pressing.

Production of cathode Cathode was prepared by adding 92% by weight of lithium cobalt composite oxide as a cathode active material, 4% by weight of carbon black as a conductive material, and 4% by weight of PVdF as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. A mixture slurry was produced. The cathode mixture slurry was applied to an aluminum (Al) thin film, which is a cathode current collector having a thickness of 20 μm, and dried to produce a cathode, followed by roll pressing.

Batteries were manufactured using electrodes and separators manufactured above.

The battery is manufactured by assembling an anode, a cathode, and a porous organic / inorganic composite separator in a stacking manner, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1/2 ( Volume ratio), lithium hexafluorophosphate (LiPF ₆ ) 1 mol) was injected.

Comparative Example 1
As shown in FIG. 4 and FIG. 5, an example was used except that the nonwoven fabric base material was made of ultrafine yarn having an average thickness of about 20 μm and the pores having a major axis exceeding 70 μm were 100%. A battery was produced in the same manner as in Example 1.

Comparative Example 2
As shown in FIG. 6 and FIG. 7, except that a nonwoven fabric base material composed of ultrafine yarn having an average thickness of about 10 μm and a pore having a major axis of less than 70 μm is about 10% is used. A battery was produced in the same manner as in Example 1.

A charge / discharge test was performed on the battery manufactured as described above, and the results are shown in Table 1.

Figure 8 is a discharge failure profile of the battery loading weight of the porous coating layer is 0 g / m ² according to Comparative Example 2, FIG. 9, loading weight of the porous coating layer in Comparative Example 1 20 g / m ² is a leakage current profile of a battery exceeding ² . On the other hand, in FIG. 10, according to example 1 loading weight of the porous coating layer and the charge and discharge path profile of the battery in excess of 5 to 20 g / m ² and 20 g / m ^2, the porous coating layer according to Comparative Example 2 The charge / discharge path profile of the battery having a loading amount exceeding 20 g / m ² is shown at the same time.

Claims (15)

A separator,
A planar nonwoven fabric substrate having a large number of pores; and a porous coating layer provided on at least one surface of the nonwoven fabric substrate and formed of a mixture of a large number of inorganic particles and a binder polymer,
The nonwoven fabric substrate is
Formed from ultrafine yarn having an average thickness of 0.5 to 10 μm,
A separator comprising 50% or more of pores having a major axis of 0.1 to 70 μm based on the total number of pores.   The separator according to claim 1, wherein an average thickness of the ultrafine yarn is 1 to 7 µm.   The separator according to claim 1, wherein a melting temperature of the ultrafine yarn is 200 ° C or higher.   The ultrafine yarn is any one kind of polymer selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, or two of these polymers. The separator according to claim 1, which is formed of a mixture of seeds or more.   The separator according to claim 1, wherein the nonwoven fabric substrate has a thickness of 9 to 30 μm. Loading weight of the porous coating layer with respect to the nonwoven fabric substrate is a to no 5 20 g / m ^2, the separator according to claim 1.   The separator according to claim 1, wherein the weight ratio of the inorganic particles and the binder polymer in the porous coating layer is 50:50 to 99: 1.   The separator according to claim 1, wherein an average particle diameter of the inorganic particles is 0.001 to 10 µm. The separator according to claim 1, wherein the binder polymer has a solubility index of 15 to 45 MPa ^1/2 .   The binder polymer is polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate. Any one binder polymer selected from the group consisting of butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan and carboxymethyl cellulose, or a mixture of two or more of these. The separator according to claim 1. A flat nonwoven fabric base material is prepared which is formed from ultrafine yarn having an average thickness of 0.5 to 10 μm and contains 50% or more pores having a major axis of pores of 0.1 to 70 μm based on the total number of pores. And a step of coating and drying a binder polymer solution in which inorganic particles are dispersed on at least one surface of the nonwoven fabric substrate. It said to have no 5 loading amount of the inorganic particles and the binder polymer for the non-woven fabric substrate formed by adjusted to 20 g / m ^2, a manufacturing method of a separator according to claim 11.   The method for producing a separator according to claim 11, wherein the weight ratio of the inorganic particles and the binder polymer in the binder polymer solution in which the inorganic particles are dispersed is adjusted to 50:50 to 99: 1. An electrochemical element,
A cathode, an anode, and a separator interposed between the cathode and the anode,
An electrochemical element, wherein the separator is the separator according to claim 1.   The electrochemical device according to claim 14, wherein the electrochemical device is a lithium secondary battery.

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